1. Field of the Invention
This invention relates to a material and a method for forming a low-dielectric-constant film which can be utilized for enhancing the function of an integrated circuit in the field of semiconductors.
2. Description of the Prior Art
For the sake of enhancing the function of a semiconductor integrated circuit, the circuit is required to lower the dielectric constant of the interlayer dielectric thereof. As a low-dielectric-constant film, the porous insulating film which has the porosity of the interior thereof exalted is widely used. The porous insulating film which is used as a low-dielectric-constant film, however, is generally problematic in betraying weak strength and high hygroscopicity owing to the configuration thereof.
As a means to solve this problem, the technique (TMCTS treatment) of thermally treating a porous silica film in the atmosphere of 1,3,5,7-tetramethyl cyclotetrasiloxane (TMCTS) has been known (Y. Oku et al., “Novel Self-Assembled Ultra-Low-k Porous Silica Films with High Mechanical Strength for 45 nm BEOL Technology,” Proc. IEDM 2003, p. 139). This technique is thought to attain enhancement of strength and hydrophobicity by inducing the Si—OH bond contained in the porous silica film and the Si—H bond in the TMCTS to react with each other during the course of the TMCTS treatment as illustrated in FIG. 1.
The elastic modulus Ew of the silica skeleton (silica wall) is theoretically thought to be successfully enhanced to approximately 70 GPa of the magnitude of the elastic modulus of the thermal oxide film. The existing Ew, however, is assumed to be approximately 40 GPa even in the champion data as illustrated in FIG. 2. Thus, the conventional TMCTS treatment is not fully satisfactory and is in need of further enhancement of hydrophobicity and strength.
The present inventors have concluded that one of the reasons for the insufficiency of the conventional TMCTS treatment is ascribable to the insufficiency of the reaction between the Si—OH group in the porous silica film and the Si—H group in the TMCTS and that a new technology is needed for facilitating the progress of this reaction. The present inventors, therefore, have taken notice of the presence of a stereoisomer in the TMCTS and have pursued a study on the molecular structure of the TMCTS stereoisomer which is thought to react readily with the Si—OH bond in the porous silica film.
This invention has been proposed in the light of the true state of affairs mentioned above and is aimed at providing a material and a method for the formation of a low-dielectric-constant film which is possessed of low hydrophobicity and excellent strength.